Temporal sequential correlation analysis on compound action potentials of the auditory nerve versus the stimulating AM-sound envelope

Compound action potentials of the auditory nerve in response to amplitude-modulating tones were recorded in guinea pigs with electrode implanted to the exit of the internal auditory meatus and temporal sequential correlation between the responses and the modulators was studied in a paradigm of systematically changing acoustic parameters. Three kinds of modulator were used:continuous or burst sinusoids of fixed frequency (in the range of 40 Hz~5 kHz),short bursts of sinusoids with changing frequency and short segments of speech signal. Ranges of parametric variation were 500 Hz~20 kHz for carrier frequency, 5%~95% for modulation depth and 20~90 dB SPL for intensity. For continuous or burst sinusoidal modulators of fixed frequencies, the correlation coefficient (r) remained quite high in most parametric conditions,amounting from 0.80 to 0.95. It became smaller mainly in instances of decreased response amplitude on account of unfavourable parameters. For burst modulators of changing frequency, r varied around 0.66~0.86. When segments of speech signal served as the modulators, significant correlation (r around 0.50) also existed, indicating the validity of the timing mode of information encoding for speech sound at the cochlear nerve level. Some theoretical and technical points in studying the timing mechanism of audition is discussed.